Dr. Noam Sobel, Ph.D. (@LabWorg) is a professor of neurobiology in the department of brain sciences at the Weizmann Institute of Science. His research focuses on the biological mechanisms of smell (“olfaction”) and how sensing odorants and chemicals in our environment impacts human behavior, cognition, social connections, and hormones.
Andrew Huberman and Dr. Noam Sobel discuss how smell is a crucial component of our social lives and interactions, the influence of smell on emotions, hormone levels, and memories, and the future of being able to send smells via the internet.
Host: Andrew Huberman (@hubermanlab)
We smell through our nose and mouth – a big part of olfaction to food and taste is through our mouth
Molecules travel up our nose and interact with receptors lining the nasal structure and eventually turn into a neural signal
To emphasize its importance, a lot of our genome is actually dedicated to olfaction
Each receptor will activate a different subset of receptors
A hit in the back of the head severs an essential component of smell and causes loss of smell, either partially or completely
If you don’t get it back within 1-1.5 years, you will never get it back
Alpha lipoic acid may recover smell, but data is mediocre at best
“Olfaction is a definite use it or lose it system” – Dr. Noam Sobel
Smell and memories are linked: first-time experience of smell develops a particularly robust memory cue
Humans can follow scent trails buried in the grass, especially if deprived of vision and other senses
Humans innately have a remarkable sense of smell but you can improve and further train your ability to smell in as little as 4 days
The human detection threshold is extremely sensitive
There’s a constant shift in our nasal cycle, how we use our nostrils from side to side particularly when sleeping– it’s driven by switches in the sympathetic/parasympathetic nervous system
You can tell the difference between adults with ADHD and not, and even whether they’re medicated just by monitoring olfaction seesaw
The nasal cycle seems to be more about brain function than actual olfaction demands
Information processing is linked to olfactory inhalation
Nose breathing shapes cognition: there is data supporting the idea that nasal inhalation is timing and modulating cognitive processing
Loss of sense of smell is a strong indicator of neurological disease and neurodegeneration – the nose is a path to our brain, loss of smell shows up in Parkinson’s and Alzheimer’s years before any other symptom
Though there are clinical tests, the problem is olfaction hasn’t been properly digitized so it’s tough to measure and link causality
Also, olfaction isn’t tested in newborns so it’s tough to measure olfaction deterioration without a baseline
People are constantly smelling themselves and others, consciously or subconsciously
You can see this clearly in dogs, when they meet they smell each other
Handshaking is sort of the human version of smelling each other – we’ll often handshake then use our hands to fix our hair or touch our nose, etc.
Studies show we even subconsciously even bring our hands to our nose and sniff after the handshake
“Click friendships”: there are people you meet and hit it off right away – the theory is a similarity in body odor may contribute to becoming fast friends
Olfaction and reproduction are linked in all mammals, including humans – romantic selection in humans is based on body odor
In pregnant female mice, a strange smell in the male’s urine can cause a miscarriage
Humans have a very high rate of spontaneous (no known reason) miscarriage – we could possibly have some trigger related to olfaction but there is nothing clearly defined yet though there are theories of relationship to olfactory memory
A specific scent of babies reduces aggression in the father and increases aggression (likely translated into protectiveness) in mothers
Women and synchronized meses: there does appear to be a chemo-signaling effect but the statistics of cyclic events are tricky and it’s unlikely chemo-signaling is the whole story
In a way, fear is contagious: we emit a specific body odor when we’re in a state of fear, and this is picked up by others in our vicinity
Most of the non-verbal communication in mammals is through scent of urine (but obviously that’s replicable in humans) – instead, tears are the human chemical signal
Tears are odorless but when sniffed, there’s a pronounced reduction in testosterone in men
The same finding was replicated in mice
Dogs also shed emotional tears
Engineered meats are looking to add the smell of real meat as a way of enticing more customers
Sense of smell is incredibly similar, in contrast to what people think – we are biased by outliers and there are some polarizing smells but in reality, people agree on 90% of odors
Sending scents through computers: Google has a well-financed startup aiming to digitize smell
COVID has caused a renaissance of olfaction research because people are more acutely aware of the importance of olfaction
It is possible to predict the odor of something measuring molecules
Articles
The Age of Olfactory Bulb Neurons in Humans (Neuron)
The Privileged Brain Representation of First Olfactory Associations (Current Biology)
Mechanisms of scent-tracking in humans (Nature Neuroscience)
Measuring and Characterizing the Human Nasal Cycle (PLOS ONE)
Human non-olfactory cognition phase-locked with inhalation (Nature Human Behaviour)
A social chemosignaling function for human handshaking (eLife)
There is chemistry in social chemistry (ScienceAdvances)
MHC-dependent mate preferences in humans (Proceedings of the Royal Society B)
An Exteroceptive Block to Pregnancy in the Mouse (Nature)
Fear-Related Chemosignals Modulate Recognition of Fear in Ambiguous Facial Expressions (Psychological Science)
Sniffing the human body volatile hexadecanal blocks aggression in men but triggers aggression in women (ScienceAdvances)
Menstrual Synchrony and Suppression (Nature)
Regulation of ovulation by human pheromones (Nature)
Human Tears Contain a Chemosignal (Science)
Why Only Humans Shed Emotional Tears (Human Nature)
Revisiting the revisit: added evidence for a social chemosignal in human emotional tears (Cognition and Emotion)
Increase of tear volume in dogs after reunion with owners is mediated by oxytocin (Current Biology)
An olfactory self-test effectively screens for COVID-19 (Communications Medicine)